Point at or tap any part to see its name. Tap the lamp, heater, or iron to switch it on or off.
The receptacles are wired one after another, but each load gets its own path from the black wire to the white. That is a parallel circuit, not a series one.
Each receptacle has 120 volts between its brass and silver screws, whether or not anything is on.
The feed wire from the breaker carries the amps for every load at once. Past each box, the cable carries less, because it only feeds the loads farther down the line. The white wire brings the same amps back.
The dots show amps. More dots passing each second means more amps. The dots do not show how fast electrons move. Real electrons in house wiring drift less than a millimeter per second, far slower than a snail.
Wall power is AC. It reverses direction 120 times a second. The dots show how much current flows as if it were steady, out on the black wire and back on the white.
The bare ground wire carries no current in normal use, so it has no dots.
Each load's amps come from its nameplate. Amps equal watts divided by volts. A 60 watt bulb draws 0.5 amps. A 1,500 watt heater draws 12.5 amps, and a 1,200 watt iron draws 10.0 amps. The heater and iron are heating elements, so their resistance stays steady at 9.6 and 12 ohms. The lamp filament is 240 ohms while lit. A cold filament has far less resistance, so the bulb draws more for an instant when it turns on.
The circuit is 12 AWG copper on a 20 amp breaker, 240.4(D)(6). The receptacles are rated 20 amps. That rating is allowed on a 20 amp circuit with more than one receptacle, Table 210.21(B)(3).
Above 20 amps, the breaker trips after a while. The Breaker and wire visual shows why.
The picture treats the wires as perfect. Real wires lose a few volts along the way.
Where the cable goes on to the next box, the hots, neutrals, and grounds are spliced with a short pigtail to the receptacle. That is trade practice. In the last box, the wires land straight on the screws.
This is a bedroom. Bedroom circuits also need AFCI protection, 210.12(B). The breaker is drawn plain to keep the picture simple. The panel gets its power from the service, which is not drawn.
Test before you touch, every time (trade practice).
The wall and boxes are shown cut open. The picture is not to scale.